Influence of contact surface roughness on interlayer shear resistance

Regarding performance of multi-layered asphalt pavement systems, interlayer bonding has an important role because it considerably influences stress and strain distribution in the pavement. Interlayer shear resistance may depend on various factors such as type and presence of tack-coat, maximum aggregate size and air void content of the two mixes in contact, as well as roughness conditions at the interface. This study, which is part of an ongoing research project, focuses primarily on the possible relationship between interlayer shear resistance and lower layer surface roughness of double-layered asphalt concrete specimens. In addition, the study deals with the comparison of different methods to evaluate this contact surface roughness. Before placing the upper layer, two different methods were applied to determine surface profiles: a laser profilometer and a profile comb. The obtained profiles were used to perform MPD (Mean Profile Depth) and fractal dimension evaluations. Moreover, the lower layer surface roughness was evaluated with the traditional sand patch method. Each technique was used to seek a relationship between the contact surface roughness and the interlayer shear resistance measured by both ASTRA (Ancona Shear Testing Research and Analysis) test device and LPDS (Layer-Parallel Direct Shear) test device. The results show that greater contact surface roughness leads to an increase in ASTRA and LPDS interlayer shear resistance in different proportions for MPD, fractal dimension and sand patch method roughness evaluation.